The subject matter disclosed herein relates to a valve assembly and, more particularly, to a valve assembly having an anti-rotation mechanism for a pitot tube.
A pneumatically actuated butterfly valve opens and closes a duct through which fluid passes from an upstream end to a downstream end. Some valves operate in accordance with a measurement of the pressure of the fluid at the upstream end. That is, when they detect that the upstream pressure is too high or beyond a predefined threshold, they close at least partially to lower the downstream pressure. By contrast, when the upstream pressure is low, they open to allow more fluid through the duct.
The upstream pressure is detected by way of a pitot tube positioned such that its tip is placed in the fluid. The pitot tube is used to communicate a sample of the fluid to a valve actuator where the fluid pressure can be extracted and a determination can be made to open or close the valve. To this end, the pitot tube has an angled tip that is designed to discourage debris from entering the tube. In order for the pitot tube to be effective, however, the angled tip must face in the reward direction and the pitot tube must be prevented from rotating. Typically, this is accomplished by the use of a high temperature adhesive, such as Stycast 2762, but it has been seen that the actual operating temperature of the fluid often exceeds this and other adhesive's capability. As such, pitot tubes often rotate to an undesired orientation.